Restarting

After finishing your first calculation or achieving the self consistency (SC), you may want to continue the calculation or to calculate density of states, band dispersion, molecular orbitals, and etc. using the SC charge in order to save the computational time. To do this, a keyword 'scf.restart' is available.

   scf.restart           on        # on|off,default=off

When the keyword 'scf.restart' is switched on, restart files generated by your first calculation will be used as the input Hamiltonian or charge density in the second calculation, while 'System.Name' in the second calculation should be the same as in the first calculation. The restart files are stored in a directory '*_rst' below the 'work' directory, where * means System.Name. The restart files in the '*_rst' contain all the information for both the density matrix mixing schemes and k-space mixing schemes. So, it is possible to use another mixing scheme in the second calculation. In the geometry optimization and molecular dynamics simulations, the restart files generated at the previous steps are automatically utilized at the next step to accelerate the convergence using an extrapolation scheme [33,34]. As an example, we illustrate the restarting procedure using a input file C60.dat which can be found in the directory 'work'. In Fig. 7, we see that the second calculation is accelerated due to the use of the restart file.

Input file for the restart calculation

An input file, *.dat#, is generated at every MD step for the restart calculation with the final structure and the same 'Grid_Origin' explained in the Sec. 'Fixing the relative position of regular grid'. Using the file, *.dat#, it can be possible to continue MD calculations and geometry optimization from the last step.

Figure 7: SCF convergence of a C$_{60}$ molecule. In the second calculation, the restart files generated by the first calculation were used. The input file is C60.dat in the directory 'work'.